The major goals of the proposed research are 1) to further clarify the normal functions of the basal ganglia in the regulation of movement and posture and 2) to study the pathophysiologic mechanisms underlying movement disorders in man. (1) Studies on normal function: (a) in the striatum, motor cortex and centre median nucleus during the performance of trained limb movements in a visuomotor tracking task and the response of these same neurons to active movement and passive manipulation outside the task. (b) in the substantia nigra and pallidum during trained head and eye movements. (2) Studies on pathophysiologic mechanisms: We propose to study in the primate: (a) the abnormal movements, the underlying patten of muscular activity in the basal ganglia in the primate model of hemiballismus produced by lesioning of the subthalamic nucleus. (b) the character of movement abnormality, the underlying pattern of muscular activity and changes in neural activity subsequent to lesioning of the striatum.